Photographic and projection lens



OR lvWfsl v MHV-w j April 17, 1934- A. wARMlsHAM 1,955,617

PHOTOGRAPHIC AND PROJECTION LENS Filed Jan. 27. 1931 D1 Dz D5 f d T1 Tx T3 Ta Tf T5 X '2 #nb x 2 0 +3 auf@ D1 D: D3

Tf Tz Ts Ta T5 T2',

R, Rz R, R, R5 RR, R5 R, Rm

D, |52 T5 A -n T2 T3) T4 D3 lr? f I INVENTOR T6 D4 R. R3 R157 R.. "l2 BY /V 24 R2 R4- R5 Re R9 Km MJ ATTORNEY 'I l g Patented Apr. 17, 1934 UNITED STATES PATENT OFFICE Arthur Warmisham, Leicester, England. assignor to Kapella Limited, Leicester, England, a corporation of England Application January 27, 1931, Serial No. 511,454 In Great Britain January 28, 1930 3 Claims.

This invention relates to photographic and projection lenses, of the Petzval type, and especially to those of modified Petzval type described in U. S. patent application Serial No. 132,591 and its continuation, Serial No. 402,837; and its object is to improve the field atness of such lenses. while still retaining the high relative aperture.

The typical Petzval lens may be improved in the above respects by constructing the divergent member of the rear component, hitherto a simple element, as a compound member comprising a highly refractive convergent member and a divergent element of lower refractive index, preferably but not necessarily cemented together to reduce the number of air-glass surfaces to a minimum.

The front component of a Petzval type lens is convergent, and hence, if the front surface of the rear component is formed concave towards the incident light, the marginal rays from the front component will strike such surface at a high angle of incidence and consequently produce a high degree of spherical aberration. According to the present invention, therefore, the front surface of the rear component is formed convex to the incident light to reduce such angle of incidence and the consequent spherical aberration.

It is also advantageous to split up the sin'gle simple convergent member of the rear component into two simple convergent lenses, and also to form the front component of two compound members, the cemented surfaces of which are dispersive.

Various forms of lenses constructed in accordance with the present invention are shown, by way of example, in the accompanying drawing, wherein:

Fig. 1 shows a lens having a front component formed of a simple convergent member and a compound convergent member, and a rear component formed of a compound divergent member and a single simple convergent member;

Fig. 2 shows a lens having a front component formed of a compound convergent member, and a rear component formed of a compound divergent member and two simple convergent members;

Fig. 3 shows diagrammatically a lens in which the front component is formed of a single simple convergent member and a compound convergent member, and the rear component is formed of a compound divergent member and two simple convergent members.

The constructions shown are merely illustrative of the various forms which may be used.

The numerical data for an objective of relative aperture F/ 1.5, constructed according to the present invention, as illustrated in Fig. l, is given below. The notation used is that the successive radii of curvature, counting from the front, are called R1, R2, etc., the sign denoting that the curve is convex toward the front, and that it is concave toward the front. The axial thicknesses of the elements are denoted by T1, T2, etc., and the separations of the members by D1, D2. etc. The material is defined in terms of the mean refractive index nn. as conventionally employed, followed by the Abbe V number, and further by the type-number in Messrs. Chance Brothers optical glass catalogue.

Equivalent focal length 1.059"

l Cllmnce ros.

D V catalogue number T1 .096 1.5735 57.5 9002 Bri-1.454

Di .002 Air Ra+ .7005

Tn .032 1.6521 33.5 5093 R-l-l. 775

D: .130 Air Rn+ .7247

T5 020 1.5635 42.9 8653 RH .3922

Da .090 Air Rq+ .7500

To 200 1.6437 48.3 Rio-2. 559

The residual Petzval curvature of the objective in this example is .696, whereas that of an objective constructed according to the specification of applications Serial Nos. 132,591 or 402,837 is .809, which shows an improvement of some twelve per cent in the residual curvature.

The numerical data of an objective of relative aperture F/ 1.4, constructed according to the present invention, as illustrated in Fig. 2, is given below. The notation of this example is the same as that used in the data above given, and the material is deilned in the same terms.

BChnce l ro ers D V catalogue number Tx .105 1. 529 51. (l 7803 Rr- 495 T2 030 1. 652 33. 5 5093 Rri- 2. 250

D1 100 Ail Bri-20. 0

Ta 082 l. 6437 48. 3 Rs- 4348 Ti 030 1. 520 5l. 6 7863 R|+ 4605 D2 050 Ail' Rz-l- 8333 T5 060 l. 6133 59. 0 4873 Ra-14. 29

D3 005 Air Ro-i- 1. 099

To 070 1. 6133 59. 0 4873 E10* 4. 268

The numeral data of an objective of relative aperture F/ 1.4, constructed according to the present invention, as illustrated in Fig. 3, is given below. The notation of this example is the same as that used in the data given for the rst two examples, and the material is defined in similar terms.

Equivalent focal length 1.00"

Ti 067 1. 613 59. 1 Rz+ l. 427

Dl 005 Ra-l- 0365 T2 257 1. 613 59. 1 Ri- 6055 Ta 029 l. 747 27. 4 Rr*- l. 039

Dz 095 :Rs-12. 72

T4 078 l. 652 33. 5 R1 4770 T5 O30 1. 613 59. 1 RH- 4990 DI 048 Rn-i- 7000 Tc 057 1. 644 48. 3 Blu-2. 385

D4 005 R11-F1. 706

T1 067 l. 613 59. 1 R11-1. 878

It will be understood that the data given in the above tables are merely illustrative of a large number of different ways in which the principles of the invention can be applied.

What is claimed is:

1. An objective of the Petzval type, in which the front component is convergent and the back component comprises two convergent elements, and a divergent member compounded of a convergent element of high refractive index cemented to a divergent element of lower refractive index.

2. An objective of the Petzval type. in which the front component comprises two convergent members, one of which is a single element and the other a compound member whose cemented surface is dispersive, and in which the back component comprises a. divergent member compounded of a. convergent element of high refractive index cemented to a divergent element of lower refractive index, such divergent member having both its outer curvatures convex towards the incident light, and a convergent member behind the divergent member.

3. An objective of the Petzval type, in which the front component consists of two convergent members. one of which is compounded, and its cemented surface is dispersive, and the back component consists of two simple convergent members, and a. divergent member compounded of a convergent element of high refractive index cemented to a divergent element of lower refractive index.

ARTHUR WARMISHAM. 

